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Old 25th January 2009, 12:58 AM   #1 (permalink)
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44 IDF troubles

Hey Guys I just fitted a brand new set of 44IDF's to my FFR Coupe
I am having some trouble which I'm hoping someone can help me with.

Ok I balanced carbs, so are all good. Set ignition timing to 14 deg.
Now the problems......
1st My front passenger carb does not seem to working like the others.
The other 3 carbs only need 1 3/4 turns out of the mixture screw to run happy but the front carb needs 3 or so turns out before it will do anything. I checked the idle jets and they all the same in the carbs. I have also blown through the idle circuit and all is clear.
2nd the front drivers carb, one of the barrels does not seem to be doing anything. You can turn the mixture screw as many times as you like and nothing changes but on the same carb the other mixture screw works fine.
I'm suspecting vacuum leaks but not sure. Driving the car it seems to go great it revs fine but only after about 1800rpm or so. Up to 1800rpm it sneezes back through the intake. While driving if you rev the engine then let the engine wind down as you slow down it pops and crackles out the exhaust.
Idle jets 50
mains 135
F11
bleeds 200
Stock standard 5.0 converted from EFI to Webers with twin side pipes.

Hoping for some guidence...
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Old 25th January 2009, 07:48 AM   #2 (permalink)
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Re: 44 IDF troubles

Vacuum leaks are the most likely cause. The usual troubleshooting method is to direct an unlit propane torch around the base of the carb and manifold and watch for changes. Set all the idle screws to 1 3/4 turns first.

After higher-speed running, are the exhaust pipe temperatures equal?
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Old 25th January 2009, 09:29 AM   #3 (permalink)
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Re: 44 IDF troubles

Sounds familiar. Check this thread, it may give you some ideas:

http://www.gt40s.com/forum/gt40-tech...arb-issue.html

To help conclude the saga noted in that thread: In the final analysis, a slight change in the idle jets (from 60 to 55), really blowing out the idle circuit from the top air port with compressed air after removing the idle jets, and adjustment of the mixture seemed to address the problem, although it has been too dang cold to follow up on the project the last couple of weeks.

I am no expert, but if an idle circuit is fouled by the smallest bit of dirt no fuel will flow, no combustion will occur, and fiddling with the mixture screw won't make much difference.

A cheap laser temp gauge aimed at a header was a quick and easy way of seeing which cylinders weren't firing. Works better than a finger. Got one scar to prove it . . . . . ( I learn quick).

Good luck.

Chuck
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Old 25th January 2009, 11:56 PM   #4 (permalink)
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Re: 44 IDF troubles

I've been reading that thread and my set up is exactly the same and it sounds like I have the same or similar trouble. My problem is idle circuit related and my jetting is very similar.

Ok , I reset the idle mixtures and idle screws with no change.
I swapped the passenger side carbies front to rear and the problem followed the carb.....although there was slight improvement in idle quality aswell and mixture adjustment.

Things I have done to help situation and noticed.
Swapped carbs around
blown out idle circuits several times. (not with compressed air)
problem follows carb
If you put your hand completely over a ram tube and block it off some cylinders will stall others it makes no difference.

Since I changed the passenger carbs around I have noticed that the drivers side carbs are not responding as they were before. I have sprayed WD40 around the base of the carbies with no change in engine speed.

Oh how testing webers can be.....
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Old 26th January 2009, 02:28 AM   #5 (permalink)
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Re: 44 IDF troubles

Ok removed offending carb, stripped and cleaned. Hi pressure air was used to blow out idle circuit including jets. I thinkn I may have a dud carb if that's possible. ....
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Old 26th January 2009, 11:23 AM   #6 (permalink)
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Re: 44 IDF troubles

Float adjusted?

Perhaps bad idle jet?
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Old 26th January 2009, 11:32 AM   #7 (permalink)
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Re: 44 IDF troubles

So the problem follows that particular carb around...is there a defect in the carb base that would cause a vacuum leak?
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Old 26th January 2009, 04:44 PM   #8 (permalink)
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Re: 44 IDF troubles

You might want to check the mixture screw profiles against each other. I bought webers that came with mismatched idle mixture screws - really tapered vs. really blunt. It is simple to check - pull the one fomr the good and the bad carbs and look at them side by side.

What are your bypass screws set to? Are they all closed?

Did you make sure your idle jet holes are clear?
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Old 28th January 2009, 07:55 AM   #9 (permalink)
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Re: 44 IDF troubles

Ok Here's the latest on my Weber saga.....

We cleaned out carbies found one blocked idle jet, Refitted everything
and still a major difference in carby response......anyway we decided to ignore setting idle screws to the same amount of turns and set each cylinder untill it picked up. Some cylinders needed only a turn and a half others needed nearly 3 turns but all cylinders where finally firing and the engine is idling as smooth as stocker should. We decided to drive the car and see what would happen.

Out on the road under light load we could here the carbs coughing back or sneezing through the intake. The car drove really well, if you put your foot down the engine will rev all the way to 5500rpm smoothly and with out hesitation or back firing / sneezing, Stamping on and off the throttle was awesome with no flat spots. What a great noise.

So all I need to do is sort the low speed/light load sneezing and the engine tune is sorted.

I think I need to go richer with the idle jets but when you hold the throttle open and the engine free revs at approx 1200rpm the exhaust makes a popping noise which indicates rich.

Another question should I connect up the vac advance?
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Old 28th January 2009, 08:34 AM   #10 (permalink)
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Re: 44 IDF troubles

I don't have an answer on this but I am interested to see what others say...both of my Ford performance engines have MSD distributors with only mechanical advance. We have had no trouble tuning them to idle smoothly and accelerate briskly. I'd guess, though, that if your distributor is set up for VA you should be using it. You might also ask the maker of the distributor. I think most high-performance engines don't have vacuum advance, but I could of course be wrong. Vacuum and mechanical advance are slowly becoming obsolete as more and more companies build programmable ignitions; the latest MSD boxes can be connected to a laptop computer and you can tailor the advance curve pretty much as you want with the computer.
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Old 28th January 2009, 01:29 PM   #11 (permalink)
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Re: 44 IDF troubles

You should sort out your distributor advance prior to messing with the carbs in my experience. Make sure you are getting the correct idle and advance timing.

Also in my experience, popping noise usually mean lean mixture - not rich. Did you happen look at the mixture screw profiles like I suggested? If they are different from screw to screw then you will have dissimilar screw positions for the same mixture in each barrel. Did you check you bypass screw positions? If those are open, by how much is each open? Did you open them to balance airflow in barrels on the low flowing barrel of each carb (i.e., is the matching barrel bypass closed)? On the weber 44 IDF, the idle circuit does it all from idle up to around 2500 rpm where the mains kick in - in steady state throttle conditions. Any throttle movement other than steady state has the accel pumps causing the main effect. Therefore, if it is popping during aacceleration, then your pumps might not be squirting enough. If it is popping during idle, then the idle circuit is lean.

Here is a link to a nice write up of dialing in weber 44s...written about dual webers, but applicable to sets. I found thi svery helpful:

Basic Jetting Theory and Procedure - Aircooled.Net Tech Article

and this is about syching them. Again, it is written for a pair, but the process works fine for sets like you have:

Carburetors 102: Synchronize Dual Carburetors - Aircooled.Net Tech Article

Please keep posting your findings...

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Old 28th January 2009, 06:50 PM   #12 (permalink)
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Re: 44 IDF troubles

I am not running vac advance. Checked all the srew profiles and tried opening and closing bypass screws to see if I could get a change. Nothing

I have synch'd the carbs using a gauge. I set a total timing of 36deg but this made a static idle of about 15 deg. Is this to much? Should I reduce static timing to 8-10 deg?

Will try richer idle jet and see how I go as when driving under light load the engine was coughing /sneezing back through the intake.

Question -can you buy a soft mount set up for IDF's?, I don't like the gaskets supplied with the carbs.
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Old 29th January 2009, 08:01 AM   #13 (permalink)
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Re: 44 IDF troubles

Went from #50 idles to #60.....Did not have to change the mixtures screws, engined seemed to idle happy, went for a drive and all the light/low down cough, sneezing was gone. I'm still not happy with the
huge difference in carby response but if it is running smooth and drives well then I can live with it. If it was a race car you would call it perfect.
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Old 29th January 2009, 12:34 PM   #14 (permalink)
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Re: 44 IDF troubles

Quote:
Originally Posted by albanygt40 View Post
I'm still not happy with the
huge difference in carby response
What do you mean here? What are you experiencing now? You are running a richer idle circuit...you didn't need to tweak the mixture screws at all?

Do you have 55 jets available?
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Old 29th January 2009, 06:40 PM   #15 (permalink)
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Re: 44 IDF troubles

On the road the carbies are fine.

I'm not happy that some carbies only need a turn and a half of mixture adjustment to get correct idle and others need 3-31/2 turns to achieve the same idle. I warmed up engine then changed from #50's to #60's ,when I started the motor it ran perfect. I started adjusting the mixture screws when I noticed that I was ending up at the same positions. Decided to go for a drive, The car drove much better than it has and the sneezing/bucking/popping was not happening anymore.
The car now drives really well. Under full load the stock engine will rev past 6000rpm.
Will make a youtube vid and post it on the weekend.

Cheers
Dave
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Old 29th January 2009, 08:50 PM   #16 (permalink)
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Re: 44 IDF troubles

Dave, how do the plugs look? You want to get a nice uniform light brown. If some are obviously darker/blacker then try leaning out that carb v. the others. Conversely, if some are a light/whitish color that's probably a lean cylinder or two.

Also, just for the heck of it, check to make sure the progression holes drilled in the throat are uniform across all four carbs. The order, size and number of progression holes has a significant effect upon the transition from idle circuit to running circuit - they are a significant control upon fuel flow as you start to crack the butterfly off idle.

I've received supposedly "matched sets" of IDFs only to find they are quite different (different progression holes) and they simply will not run smoothly together.
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Old 30th January 2009, 06:49 AM   #17 (permalink)
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Re: 44 IDF troubles

Went for another good run....I'm going to get arrested....Pulled plugs and
checked them out ,only 2 or 3. The electrode is a light brown and the porcelin part of the plug is light grey almost black.

Will pull all plugs, replace them and recheck.
Question- If I had/have a vac leak after a considerable idle period would the plugs that have the carbs with vac leaks turn light white or be different in colour to the carbs that are running well?
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Old 30th January 2009, 08:58 AM   #18 (permalink)
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Re: 44 IDF troubles

Dave:

Reading through the thread, it would seem that the issues were (1) dirt in the idle circuit and (2) change in the idle jets. Am I reading this right? Glad you got the issue resolved.
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Old 30th January 2009, 06:48 PM   #19 (permalink)
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Re: 44 IDF troubles

One carb had one blocked idle circuit.
The issue of different idle mixture screw settings is still there, some are 1 1/2 turns others are 3 1/2 turns. Car is driving ok on the idle circuit so have settled on what it is.
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